Update: This was all due to a stupid error: previously, I had defined a method with the same name as one of the methods ActiveRecord creates, which was masking the proper behaviour and breaking everything. I can't answer/close the question for a few more hours, apologies to anyone who looked into this!
I have an infuriating problem with a has_many, :through => relationship in my Rails 3.1 app.
It is infuriating because as far as I can see it is identical to two similar relationships which both work.
The owner of these relationships declares them like this:
has_many :user_skills, :dependent => :destroy
has_many :skills, :through => :user_skills
has_many :user_roles, :dependent => :destroy
has_many :roles, :through => :user_roles
has_many :conversation_users
has_many :conversations, :through => :conversation_users
(I am aware I have not followed standard nomenclature for join tables here - I only read about the convention of both-plural, names-alphabetical after setting this up, and I will refactor later)
The first two pairs of relationships (skills and roles) work just fine.
The final relationship (conversations) does not work fully. user.conversation_users returns the expected array, but user.conversations returns nil. Not an empty array, nil.
I may well be doing something stupid here, so I would be very grateful to anyone who can spot something wrong with the ConversationUser or Conversation models below.
conversation_user.rb
class ConversationUser < ActiveRecord::Base
belongs_to :user, :inverse_of => :conversation_users
belongs_to :conversation, :inverse_of => :conversation_users
validates_presence_of :user
validates_presence_of :conversation
end
conversation.rb
class Conversation < ActiveRecord::Base
has_many :messages, :dependent => :destroy
has_many :conversation_users, :dependent => :destroy
has_many :users, :through => :conversation_users
validates_presence_of :unique_id
end
(I am also aware that these are not really complex enough to justify has_many, :through => over has_and_belongs_to_many, but planned additional functionality will require join models.)
Answering to close question:
This was all due to a stupid error: previously, I had defined a method with the same name as one of the methods ActiveRecord creates, which was masking the proper behaviour and breaking everything.
Related
I am designing a database of woodwind instrument sounds, and would like to create a table that joins pairs of sounds that a performer can combine into, for example, a trill. Such relations are transitive: if sound A has a 'Sound Relation' with sound B, then sound B has that same 'Sound Relation' with sound A.
I am familiar with join tables, but I've never seen them used to join 'like' objects, only to join 'unlike' objects, such as tags and posts, so I'm wary of going that direction.
I realize the example below looks extremely dubious, but it gives an idea of what I'm after. What is a better way of doing it? (Using ActiveRecord syntax)
Models
class Sound < ActiveRecord::Base
has_many :linked_sounds, through: :sound_relations, class_name: "Sound", foreign_key: ???
end
class Sound_Relation < ActiveRecord::Base
has_many :sounds
end
Migration
class CreateSoundRelations < ActiveRecord::Migration
def change
create_table :sound_relations do |t|
t.integer first_sound_id # This cannot possibly be right.
t.integer second_sound_id # Surely the transitivity of the
# relationship should be more evident?
end
end
end
You might try something like:
class Set < ActiveRecord::Base
has_many :sound_sets
has_many :sounds, :through => :sound_sets
end
class SoundSet < ActiveRecord::Base
belongs_to :sound
belongs_to :set
end
class Sound < ActiveRecord::Base
has_many :sound_sets
has_many :sets , :through => :sound_sets
has_many :set_sound_sets, :through => :sets , :source => :sound_sets
has_many :set_sounds , :through => :set_sound_sets, :source => :sound
end
So, no more "sound_1" and "sound_2" ... they are both just sounds. For every sound you can also use the set_sounds method to retrieve all of the sounds associated with it.
This would also allow more than two sounds in a relation, and you might like to put a "type" on the sets model.
Edit: If you look at the query generated, you'll find that sound_sets is mentioned in there twice, once with a different alias. The key to eliminating "self" joins is to include a clause in the association along the lines of:
has_many :set_sounds ,
{where("sound_sets.sound_id != set_sound_sets_sound_set_sounds.sound_id")},
:through => :set_sound_sets,
:source => :sound
... where "sound_set_sounds" is the table alias. If you can post the query in the comments I can update this with the actual alias.
I'm having the following problem while trying to model my application, it's basically a functionality to handle bills with multiple people, like sharing the rent or any other similar stuff, the deal is:
I have a user model and a billing model but can't find out how to build the associations.
A user has_many billings and billings belongs_to user but, also the billing has_many users, e.g. Tom registers a bill that is meant to be shared by Tom himself, Betty and Bob.
So that makes Tom the creditor and the other two become debtors in the billing.
I'm kinda lost at this point, how to consolidate these associations, dunno if any more information is needed or if it's clear enough, but will appreciate any help and update with any other information needed.
Thanks in advance,
---EDIT---
I've come to the following approach:
Class User < ActiveRecord::Base
has_many :billings, foreign_key: "creditor_id", dependent: :destroy
end
Class Billing < ActiveRecord::Base
belongs_to :creditor, class_name: "User"
has_many :debts, dependent: :destroy
end
Class Debt < ActiveRecord::Base
belongs_to :billing
has_one :user
end
I also tried to graphically model it for better understanding here: imgur
Would that all be correct?
Don't be afraid to use the options available to you in ActiveRecord. If your model naming is getting cluttered (Billing belongs to a User and has_many Users) then be more specific with the association labels and sort the links with options. The Rails Associations Guide is easy to Google and covers pretty much everything.
class User < ActiveRecord::Base
has_many :billings, :foreign_key => 'creditor_id'
has_many :debts, :through => :debtor_users, :source => :billing
end
class Billing < ActiveRecord::Base
belongs_to :creditor, :class_name => 'User'
has_many :debtors, :through => :debtor_users, :source => :user
end
class DebtorUser < ActiveRecord::Base
belongs_to :billing
belongs_to :user
end
You can extend the Billing model to have multiple creditors also simply by converting the belongs_to association into a has_many :through association following the same pattern as debtors just with a different join model (say CreditorUser).
I need a player to have many structures and the structure to belong to the player. Structure is a polymorphic relationship.
class Player < ActiveRecord::Base
has_many :player_structures
has_many :structures, :through => player_structures
end
class PlayerStructures < ActiveRecord::Base
belongs_to :structure, polymorphic: true
belongs_to :player
end
class StructureA < ActiveRecord::Base
has_one :player_structure, :as => :structure
has_one :player, :through => :player_structure
end
class StructureB < ActiveRecord::Base
has_one :player_structure, :as => :structure
has_one :player, :through => :player_structure
end
But if I pull out Player.first and ask for its structures, it gives:
ActiveRecord::HasManyThroughAssociationPolymorphicSourceError: Cannot have a has_many :through association 'Player#structures' on the polymorphic object 'Structure#structure'.
But it should be able to generate a SQL query where it finds all player_structures with its id, then fetches the structure based on the structure_id and structure_type. Why does this fail and how can I validly construct a polymorphic join table?
UPDATE
If I do what I want it to do manually, it works:
player_structures.collect(&:structure)
Rails, y u no do that?
I think you need to be more specific in defining your relationships in your Player model. For example:
class Player < ActiveRecord::Base
has_many :player_structures
has_many :structureas, :through => player_structures, :source => :structure, :source_type => 'StructureA'
has_many :structurebs, :through => player_structures, :source => :structure, :source_type => 'StructureB'
end
Then you can make a method that'll return all the structures defined in the relationships instead of having to access each one individually.
I have two resources that I'm trying to join - Package and Listing through a join table SubmittedPackage. I'm using Ruby 1.9.3-p125 and Rails 3.2.1 with PostgreSQL 9.1.3. The models look as follows.
class Package < ActiveRecord::Base
has_many :submitted_packages
has_many :listings, :through => :submitted_packages
class Listing < ActiveRecord::Base
has_many :submitted_packages
has_many :packages, :through => :submitted_packages
class SubmittedPackages < ActiveRecord::Base
belongs_to :package
belongs_to :listing
In Rails Console I keep getting NameError: uninitialized constant Listing::SubmittedPackage
If I replace the SubmittedPackage resource with Drum it will work (this of course includes having the appropriate table created and so forth).
Is :submitted_packages in conflict with something in Rails or ActiveRecord?
Any ideas why this is breaking?
Thanks in advance!
UPDATE: As a work-around I explicitly defined the :class_name for the has many relationship in the Listing and Package model. This has at least gotten things working, however, it's still is unclear to me why it was necessary to begin with. What Rails or Ruby naming convention was being broken by :submitted_packages ?
class Package < ActiveRecord::Base
has_many :submitted_packages, :class_name => 'SubmittedPackages'
has_many :listings, :through => :submitted_packages
class Listing < ActiveRecord::Base
has_many :submitted_packages, :class_name => 'SubmittedPackages'
has_many :packages, :through => :submitted_packages
class SubmittedPackages < ActiveRecord::Base
belongs_to :package
belongs_to :listing
If SubmittedPackage is the JoinTable, I guess it should have many listings, but I'm seeing just many packages and many submitted_packages.
HTH
There are Things in Places which I'm looking to find. One Thing could be in many different Places, and many Things can be in one Place.
class Thing < ActiveRecord::Base
has_and_belongs_to_many :places
end
class Place < ActiveRecord::Base
has_and_belongs_to_many :things
end
I want to record the Finds of my Users so that I know where they found what.
class Find < ActiveRecord::Base
belongs_to :user
belongs_to :places_thing # Is this depluralization correct?
end
class User < ActiveRecord::Base
has_many :finds
# Now, how can I link in the Things the user has found? Like this?
has_many :found_things_in_places, :class_name => :places_things, :through => :finds
has_many :things, :through => :thought_things_in_places
end
Does this seem right? is it efficient? Thanks.
I think you were on the right track, the big change I'd make is that rather than having a join table (places_things) you should make it a proper model. I decided to call this an existence.
The data only exists in one place, so it's properly normalized. These relationships are clear and will be easy to manage. I think it's efficient.
class Place < ActiveRecord::Base
has_many :existences
has_many :things, :through => :existences
end
class Thing < ActiveRecord::Base
has_many :existences
has_many :places, :through => :existences
end
class Existence < ActiveRecord::Base
belongs_to :place
belongs_to :thing
end
class Find < ActiveRecord::Base
belongs_to :user
belongs_to :existence
end
class User < ActiveRecord::Base
has_many :finds
has_many :existences, :through => :finds
has_many :things, :through => :existences
end
You'll need rails 3.1 to do the nested has many through's like we did in User.
BTW the correct association declaration should be: belongs_to :places_things